The fashioning of a large number of contiguous beams involves making an antenna comprising a large number of elementary radiating elements, placed in the focal plane of a parabolic reflector, the spacing of which depends directly on the angular gap between the beams. The volume allotted for the installing of a radiofrequency RF chain responsible for ensuring the transmit and receive functions under circular dual-polarization is bounded by the radiative surface of a radiating element, in the case of a multibeam application.
In the commonest configuration where each source, consisting of a radiating element coupled to a radiofrequency chain, fashions a beam, also called a spot, each beam formed is transmitted for example by a dedicated horn constituting the elementary radiating element and the radiofrequency chain carries out, for each beam, the transmit/receive functions in mono-polarization or in dual-polarization in a frequency band chosen as a function of the requirements of the users and/or operators. Generally, a radiofrequency chain comprises chiefly an exciter and waveguide paths, also called recombination circuits, making it possible to link the radiofrequency hardware components. To fashion a circular polarization, it is known to use an exciter comprising an orthomode transducer known by the acronym OMT (standing for OrthoMode Transducer) connected to an elementary radiating element for example of horn type. The OMT feeds the horn (in transmission), or is fed by the horn (in reception), selectively either with a first electromagnetic mode exhibiting a first polarization, or with a second electromagnetic mode exhibiting a second polarization orthogonal to the first. The first and second polarizations, with which are associated two electric field components, are linear and called respectively the horizontal polarization H and the vertical polarization V. The circular polarization is produced by associating the OMT with a branched coupler (also known as a branch line coupler) responsible for placing the electric field components H and V in phase quadrature. The search for a compact solution leads to grouping the radiofrequency hardware components and the recombination circuits of the radiofrequency chain on several levels stacked one below another, as represented for example in FIGS. 1a and 1b described hereinbelow. However, the higher the number of beams, the greater the complexity, mass and cost of the radiofrequency chain. To further decrease the mass and the cost of a radiofrequency chain, it is therefore necessary to modify its electrical architecture.